A treadmill workout can be a supereffective way to blast fat and tone up—as long as you know how to optimize the machine. "Most individuals believe that going as hard as you can, for as long as you can, will give the best results in weight loss, but you will actually burn more calories with a workout where you push hard, but not all the time," says Anna Sidorenko, personal trainer at Healthworks in Chestnut Hill, Massachusetts.

Your Rate of Perceived Exertion (RPE) scale measures how difficult an exercise is for you and will help you determine whether your heart rate is in the right zone. Everybody's RPE scale is different. But the beauty is, you don't need fancy equipment to figure it out—you just need to listen to your body. Hop on the treadmill and see how certain speeds affect you. Take a break, then hop on again—this time, try out different inclines. What speed or incline renders you unable to talk? That would be your RPE of 10. At what speed or incline are you barely exerting any energy? That would be your RPE of 0. Use these first two workouts to map your range:

RPE

I feel like…

My Speed (how fast can I go and still feel this way?)

My Incline (how steep can I go and still feel this way?)

0
Nothing

I'm barely moving.

1
2
Very Light

I'm just strolling. Breathing is easy. No noticeable increase in heart rate.

3
4
Light

Breathing is getting a little harder. But still, no sweat! Well, maybe a little sweat. Talking is easy.

5
6
7
Moderate

I can feel my heart working now. I'm sweating a little bit more but can talk with relative ease.

8
9
Hard

My heart is at its max rate. I'm sweating but I can talk…though I don't really want to.

10
Very Hard

My heart is racing and speaking is difficult. It's taking all my concentration to keep up with the treadmill.